A method of this kind is known from Dutch patent application no. 9400225 filed in the name of the present applicant. According to the method of manufacturing a stamper described therein, a photoresist film is applied to a stamper plate, after which the applied photoresist film is structured. The structuring of the applied photoresist film comprises the successive selective exposure and development of the applied photoresist film, wherein the structuring of the applied photoresist film furthermore comprises, in particular as an additional step, the heating of the selectively exposed photoresist film. In addition to that, the structuring of the applied photoresist film furthermore comprises the integral exposure of the photoresist film prior to developing the photoresist film. The successive steps of selective exposure, heating and integral exposure prior to the developing step are also known as “image reversal process” to those skilled in this field of the art. According to the example carried out in said Dutch patent application, a negative photoresist was coated, by means of spin-on deposition, onto a blank 300 μm thick nickel shell, which was glued on a standard 8-inch CD glass substrate for this experiment. After dry-spinning of the nickel shell/glass substrate assembly at a constant temperature of 80° C., the applied negative photoresist film was dried. After cooling, the assembly was exposed by means of a master registration system (MRS) at a wavelength of 459 nm. Directly after said exposure, the assembly was heated and subsequently cooled, after which integral exposure took place for 4 minutes. Thus, the non-exposed parts of the negative photoresist film applied to the nickel shell were exposed as yet. The assembly was subsequently developed and heated again, in the same manner as after the exposure, for the purpose of fixating the structure of the photoresist posts, after which cooling took place, with this difference that the oven temperature set for heating was now 140° C.
In practice, however, this latter heat treatment, also called hardbake, has been carried out at a temperature of 200° C. the last few years. A drawback of this relatively high temperature of the final heat treatment is the fact that the so-called photoresist posts formed after the developing step lose their structure or geometry in an uncontrolled manner, as a result of which they will flow out more or less. Since the geometry of the photoresist posts will change as a result of the necessary heat treatment at a high temperature, the obtained stamper often does not meet the precise specifications that are required for producing optical discs, which is undesirable.